In preparing photographic materials for production and research it is necessary that such preparation and storage be in the dark as the materials are light sensitive. In the formation of photographic products the predominant light-sensitive material is silver halide that provides light sensitivity for image recording by the photographic products. These silver halide crystals are normally formed and stored in a gelatin solution in the dark. During the storage of such materials it is sometimes necessary to add liquids to the stored silver halide and gelatin emulsion. Therefore, there is a need for caps for containers containing silver halide emulsions to have the ability to pass liquids into and gases out of the container to facilitate treatment of the emulsions without the necessity of going into a dark area.
There is disclosed in French Patent Publication 2,674,038 (Heimroth et al.) daylight type cap containing labyrinth passages for addition of liquids with the simultaneous exit of air displaced by the addition of liquid.